Railroad tank cars haul numerous commodities that are difficult to clean from the railroad car. These include, for example, oil and asphalt Traditional cleaning methods require that a technician enter the tank while equipped with personal protective equipment. The technician cleans the tank by physical scraping using a pick and shovel This method generates waste material consisting of the removed remnants of the commodity. The method also is extremely time consuming and expensive, both in cost of cleaning and in loss of use. Typically, cleaning asphalt from a tank car takes three to four days.
Automated systems can eliminate the need for a technician to enter the tank in some cases. For example, some commodities can be removed by scrubbing action of a spray consisting of a solvent such as water or common cleaning solutions. U.S. Pat. No. 6,021,793 to Moulder shows an example of an automated high pressure fluid spray system for cleaning tank cars. While the mechanisms of the spray device are the primary subject matter of Moulder's invention, the state-of-the-art in chemical solvents and washes are listed to be water, diesel fuel, terpine hydrocarbon, and caustic soda. However, using solvents and solutions can compound the problem of waste disposal by increasing the volume of waste for disposal. In addition, an automated washing system offers little chance of recovering the commodity for reuse.
Various other solvents and cleaning compounds have been developed for treating vessels in which petroleum products have been processed, stored, or transported. U.S. Pat. No. 5,356,482 to Mehta et al. discloses a process for cleaning chemical process tanks and petroleum tanks, primarily by removing benzene, so that workers can enter the ranks for further cleaning and maintenance. The residual contents of the tank must be tested to identify the chosen contaminant. Then, a suitable extractant and a surfactant are applied to the vessel by vaporizing them and applying as a fog or in conjunction with steam. Possible extractants are limonene, various terpenes (dipentenes, cinenes, cajeputenes, diamylenes, oils of bergamot, geranium, citronella, dill, and caraway); and related terpenes such as hermiterpenes (isoprenes), sesquiterpenes (caryophyllenes), diterpenes, and polyterpenes. U.S. Pat. No. 5,611,869 to Hart proposes to clean refinery vessels by using an aqueous solution of alkylphenol-formaldehyde resin alkoxylate, a poly(ethylene glycol)dialkyl ester, and a solvent of C1 to C8 alcohol, glycol, and glycol ether. Such discoveries of improved solvents are beneficial for better cleaning sludges from storage tanks and rail cars, but the proposed cleaning methods offer no solution to the ever increasing volume of waste product sent to landfill.
Several systems have been proposed for treating sludges and recovering at least some of the products of the cleaning in characterized batches, such as aqueous product and hydrocarbon product U.S. Pat. No. 5,085,710 to Goss shows such a system for recovering from oil storage tanks by treating the sludge with an aqueous cleaning solution of a non-ionic surfactant consisting of C8 to C12 alkyl-phenol-ethylene oxide adduct and some combination of castor oil-ethylene oxide adduct and C8 to C12 aliphatic ethylene oxide adduct. Then a diluent such as diesel or light oil is added to the tank to recover the hydrocarbon. Upon heating the tank, hydrocarbon from sludge rises through the cleaning solution and enters the diluent. The hydrocarbon loaded diluent is removed and sent to a crude unit. The water layer is removed to a separator. Residual solids are removed by a vacuum truck. The gross products fall into three categories as the recovered hydrocarbon, the aqueous stream that perhaps can be treated in a waste water plant, and residual solids that are land-farmed. U.S. Pat. No. 5,762,719 to D'Muhala et al discloses cleaning petrochemical equipment and rail cars with a cleaning composition that is non-hazardous, biodegradable, later can be mused, and requires no steam. The composition is 20-50% terpene-based, 20-40% alkyl pyrrolidone, and 5-40% surfactant. After use, the cleaning composition is separated from the contaminant and reused. The specific protocol is spraying the contaminated object with the composition, rinsing the object with water, and separating the cleaning composition from the contaminant by heating. Cleaned contaminants include asphalt. U.S. Pat. No. 6,120,680 to Campbell suggests cleaning hydrocarbon sludges by demulsifying and liquefying them to allow separation into water, oils, and solids. The preferred demulsifier is an amine salt of dodecyl benzyl sulfonic acid (DDBSA). The preferred liquefiers are glycol ethers, polymerized glycol ethers, or polyalkylene glycols. The liquefaction of sludge with high asphaltene content is aided by addition of terpenes, especially citrene. The oil and water layers were recovered and disposed of. U.S. Pat. No. 6,168,708 to Burbridge et al discloses a cleaning method in which a hydrocarbon residue is added to a heated solvent to liquify it, after which the liquified residue is removed as hydrocarbon product. The solvent may be gas oil, diesel oil, stove oil, toluene, cyclohexane, naphtha, or xylene. Dirt and other solids accumulate in the solvent tank and are conventionally removed daring ordinary cleaning.
The practical problem resulting from all known solvent-based cleaning systems can be exemplified using data extracted from the Campbell patent, which appeared to be among the most conservative users of solvent. One of the examples mentions a 200,000 bbl storage tank that was cleaned of 25,000 bbl of sludge. The Campbell cleaning method increases this volume by solvents totalling 6%-7% of the sludge volume, which adds 1700 bbl, more or less, leading to a disposal volume on the order of 27,000 bbl of waste product per tank cleaning. From a time perspective, the tank cleaning required “only six days,” which in absolute terms remains a very long time. The removed products had to be disposed of as oil field waste, adding an incredible volume to landfill and at an unreported cost that, nevertheless, is known to be a very high figure. Many of the tank cleaning technologies proportionately use substantially more solvent than reported by Campbell, and many use steam and water for parts of the cleaning, which greatly increases the waste volume directed to landfill. Unquestionably, the environmental and financial cost of such solvent cleaning systems is high. This cost is paid by the public, both in the detriment of ever expanding landfills, the monetary costs of maintaining a federally approved landfill, and in the overhead costs necessarily charged by the storage tank owner and passed-through to the public in the costs of petroleum products and generated energy.
The Campbell patent postulated that an extracted oil layer had suitable characteristics that it could have been sent to a refinery for processing. While this postulation might have theoretical merit, it is a practical fiction. No known refinery willingly will accept sludge or diluted sludge as an input stream. To do so would risk the refinery equipment. Refineries themselves do not reprocess even their own sludges or diluted sludges; and most certainly they will not process sludges from other sources. Removing sludges in dilute condition from petro-chemical equipment may produce conveniently clean equipment, but the environmental and financial costs remain high and are further increased by the addition of solvent volume and water volume to the sludge volume.
Automated equipment, specialized solvents, and limited degrees of reclamation have been developed, but it remains an environmentally necessary goal to achieve the substantially full recovery and recycling of cleaning solutions and petroleum products from all types of process vessels, storage tanks, and transportation vehicles.
In particular, prior art systems have too often sought to produce waste streams that merely were clean enough to be accepted into landfills and waste water systems. The product of various cleaning systems almost always must be disposed of, rather than redirected into commercial use.
A closed loop or substantially self-contained cleaning system is highly desirable in order to protect water supplies from contaminated wash liquids and protect landfill sites and other disposal sites from large volumes of contaminated water, contaminated solvents, sludges, and other byproducts of petro-chemical storage, transportation, and processing.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, the method and apparatus of this invention may comprise the following.